U.S. Pat. No. 3,826,202, July 10, 1974, shows a railway vehicle truck of the type which has become known as the "Pioneer" truck which was disclosed in U.S. Pat. NO. 2,908,230, Oct. 13, 1959, these trucks having considerable permissible frame weave through elastomeric bearing bushings or sleeves around the bearing assembly. These elastomeric bearing bushings formed noise and vibration barriers between the wheel-axle units and the truck frame and car body while maintaining the truck frame position on the axles. However, the elastomeric bushings did not provide as free vertical weaving movement as might be desired.
Full solid elastomeric bushings or sleeves, such as were used in earlier constructions had a very high spring rate, that is load in pounds to deflection inches, in the range of about 200,000 to 500,000, so had little effect as spring supports, serving mainly to reduce the transmission of higher frequency vibrations and noises from the wheels to the truck frame and vehicle body while permitting truck frame weave. Such solid elastomeric bushings or sleeves acted more like a confined liquid than a real spring.
There have been proposals for modifying the elastomeric components to provide better spring action but requiring auxiliary metallic means for limiting extreme axial movement and further auxiliary means for cushioning lesser axial movements.